The Collaborative International Dictionary of English v.0.48:

Portent \Por*tent"\ (?; 277), n. [L. portentum. See Portend.]
   That which portends, or foretoken; esp., that which portends
   evil; a sign of coming calamity; an omen; a sign. --Shak.
   [1913 Webster]

         My loss by dire portents the god foretold. --Dryden.
   [1913 Webster]

WordNet (r) 3.0 (2006):

portent
    n 1: a sign of something about to happen; "he looked for an omen
         before going into battle" [syn: omen, portent,
         presage, prognostic, prognostication, prodigy]